The present invention relates to stationary seals and more particularly to a unique multiple seal type stationary sealing ring.
Various forms of sealing arrangements have heretofore been proposed for use in generally nonrotating, nonreciprocating, or stationary applications. One form of such seal is the so called multiple seal or Multiseal type sealing ring sold under the trademark Multiseal. This ring has been employed for essentially low temperature applications such as those wherein the operating conditions are less than 250.degree. F. Such a ring includes a plurality of stacked, annular split ring segments having overlapping ends and an expander. The expander acts against the segments each of which forms a seal with a surface. Heretofore, the expander employed with such rings has been a radially corrigated, wavy or hump type expander. The segments have typically been fabricated from a high carbon steel which is acceptable for the typical low temperature environment.
The multiple seal ring effects a seal between one part which is typically designated a carrier and has a ring groove formed therein and another part which overlaps the carrier, is generally circular in section and which is typically referred to as a housing. The ring groove formed in the carrier typically has upper and lower sides and a bottom or generally cylindrical wall. The parted segments are disposed within the carrier groove and the expander engages the ring groove bottom and biases the segments into engagement with the inner circumference of the housing. A multiple seal type stationary sealing ring possesses certain inherent design advantages primarily related to compactness, ease of assembly and reduced manufacturing costs which makes it particularly desirable.
In typical high temperature applications, such as in turbines, exhaust systems and the like, the heretofore available multiple seal rings have not been usable. The operating temperatures in such applications may vary from 300.degree. F. to 1600.degree. F. The high carbon steel which has been employed to fabricate the split segments and the wavy expander oxidizes at the high temperatures. This results in the segments sticking together and sticking to the sides of the carrier groove. Such sticking makes the seal essentially inoperative to properly seal the two to three atmospheres of pressure existing in such environments. Further, in such environments the carrier part is typically subjected to significantly higher temperatures than the housing part. The parts and the ring, due to the temperature differences, will expand at different rates. A sealing ring used in such applications must be able to accommodate this difference in thermal expansion. As a result of these problems, bellows type face seals, for example, have been employed. These seals are relatively expensive and bulky which presents problems for the turbine and exhaust system designer.
Merely changing the material employed to fabricate the segments and the expander of the previous multiple seal type sealing ring does not adapt this ring for use in such high temperature environments. In order to operate, the wavy expander must contact the bottom of the groove. As the carrier expands and the temperature reaches operating conditions, the wavy spring or expander takes a substantial set and fails for lack of tension. The expansion of the parts reduces the compressed height of the expander at operating conditions, raises stress levels and an excessive set typically occurs. This set reduces the radial tension exerted on the segments at operating temperature and thereby reduced the effectiveness of the sealing ring.